The present invention relates to throwing wheels, sometimes referred to as blasting wheels or shotblast wheels, used to project streams of particles against work pieces to subject the work pieces to cleaning, abrading or peening action or the like. A typical wheel of this kind is shown in U.S. Pat. No. 5,476,412. Among the objects of the present invention is an improved apparatus for and method of connecting blades to a single wheel plate or to a set of interconnected wheel plates for a centrifugal blasting wheel.
Airless centrifugal throwing wheels of the type described consist of a single or double wheel plate having a number of blades extending radially from the wheel plate(s) in equally circumferentially spaced apart relation, with a means of removable securing the blades between the wheel plate(s). In operation, the bladed wheel is rotated at high speed about a central axis and abrasive particulate material is fed onto the inner portions of the blade whereby the material is displaced by centrifugal force outwardly over the surface of the blades and projected at high velocity from the ends of the blades.
Blades of this type typically wear out under the abrading effects of the particles that are thrown. These abrasive particles move along the blades and gradually wear out portions of the throwing wheel as well as the blades themselves. Further when the particulate that is being used needs to be changed to a different material either in abrasiveness or otherwise, or when the blades become worn, the blades need to be removed and the equipment needs to be reset.
Because of the tolerances of blade casting, as well as wearing of the channel slot in the wheel and connecting member projecting from the blade through use, the channel slot is or becomes larger than the blade connecting member. This results in a sloppy fit of the blade to the wheel allowing minute particulate to work its way into the blade mounting channel which tends to seize the blade to the throwing wheel, typically referred to in the industry as “shot locking”.
This “shot-locking” makes removal of the Blades difficult and includes potential safety issues as the blades may require substantial force to remove. Typically in order to remove a prior art blade, significant downward striking force is required, such as with a hammer. blades are typically constructed of cast white iron or high chrome iron, which is very brittle, and can crack or chip when struck. These chips at times “splinter” and can cause safety issues for operators and/or damage to other wheel components.
In many prior designs, blades must be “hammered” out of the corresponding wheel channel the entire length of the blade locking connection before the blade can be removed.
Many connecting methods have been devised to attach blades to wheel plates. Some methods requires pins, springs or other mechanical locking devices. One such method is disclosed in U.S. Pat. No. 2,869,289 which utilizes leaf springs to attach the blades to the wheel. The prior art also used a stop member that was inserted through the wheel to prevent the blades from moving radially outward. In addition to stopping the blade from movement, the stop members are used to properly position the blades in the wheel to allow for proper balancing of the rotating wheel. Because of the complexity and precision needed to properly install the blades, installation of the blades in the prior art is time consuming and difficult. Further the stop member is subject to failure and damage more quickly then the surrounding structure.
Another such connecting method is described in U.S. Pat. No. 5,476,412. The prior art utilizes a simple dove tail design that narrows along the blade connecting member, that corresponds with the connecting channel to the outer section of the rotating wheel. The centrifugal outward force keeps the blades in place while the wheel rotates. The prior art uses a trapezoidal design that creates parallel surfaces between the blade and wheel. The prior art design requires the blade to “wedge” into the “V” groove channel of the wheel. Due to difficulty in casting this prior art blade, actual blade location in the wedge can vary causing the wheel to be imbalanced even with new blades. As with other prior art, this design also suffers from issues of “shot-locking” as described above.